Sent in by Code Hunter
Successfully complete story mode with Wario on the normal, hard, or super
hard difficulty setting without losing once. After defeating Rudy, you will
battle Metal Mario. Defeat him without losing to unlock Metal Mario in "VS."
modes. Note: Using the "Redo" option on the pause menu is counted as losing.

Sent in by Code Hunter
Successfully complete story mode with Dr. Mario on the normal, hard, or
super hard difficulty setting without losing once. After defeating Rudy, you
will battle Vampire Wario. Defeat him without losing to unlock Vampire Wario
in "VS." modes. Note: Using the "Redo" option on the pause menu is counted
as losing.

Sent in by Code Hunter
At the character selection screen in "VS." mode, highlight a character. Hold
L and press A to increase the computer A.I. of that character one star to
"Hard". Hold L and press B to increase the computer A.I. of that character
two stars to "S.Hard".